Emulsion polymerization of styrene



iatented Feb. 7, 1950 UNITED or STYRENE Edmond F. Fiedlcr, Adams, andGlennard B. Lucas, Pittslleld, Mass., assignors to General ElectricCompany, a corporation of New York I No Drawing. Application April 24,1948,

. Serial No. 23,128

, l I r a This invention is concerned with a method for makingpolystyrene. More particularly, the invention relates to a method forpreparing a crystal-clear polystyrene free of discoloration and having aheat distortion value of at least 90 0., which method comprises heatingan emulsified mass comprising (1) styrene, (2) water, (3) a fatty acidcomponent selected from the class consisting of (a) myristic acid, (b)palmitic acid. stearic acid, and (d) mixinires of long chain fatty acidscomprising saturated aliphatic monocarbonlic acids having an even numberof carbon atoms and'containlng from 12 to 18 carbon atoms (e. g.. lauricacid, myristic acid, palmitic acid, and stearic acid) whose averagemolecular weight is equal to from at least 210 to below 284, (4) analkali-metal hydroxide sufllcient to neutralize at least 90 per cent ofthe acids of (3), and (5) a polymerization catalyst comprisingl-hydroxycyclohexyl hydroperoxide-l.

One of the objects of this invention is to prepare an acceptablepolystyrene by emulsion polymerization which is equal to or better inmany respects to polystyrene prepared by casting.

Another object of the invention is to prepare by emulsion polymerizationa polystyrene free of objectionable color.

q A further object of the invention is to prepare a polystyrene havingimproved mechanical and heat distortion properties.

A still further object of the invention is to prepare polystyrene inrelatively short periods of time, and in good yields, and whoseproperties can be reproduced easily. I

Additional objects of this invention will become more apparent as thediscussion thereof proceeds.

The most important present day technique for manufacturing polystyrenefrom monomeric styrene having good clarity and substantially free ofdiscoloration involves casting the monomer in bulk in the presence of asuitable catalyst while at the same time heating the mass. Thisprocedure has heretofore been found essential in order to obtain apolystyrene which is substantially free of color, which is crystal-clearand water white, and which has a sufliciently high molecular weight soas to give satisfactory mechanical strength and heat distortion values.Although attempts have been made to prepare such polystyrene by othermethods, for instance, by means of emulsion polymerization, nevertheinthe polystyrene as a result of the emulsion polymerization; to diminishthe coloring of the 12 Claims. (,Cl. 260-935) polystyrenewould requireexpensive and complicated procedures which would make such productiontechniques uneconomical.

We have now discovered that we are able to prepare polystyrene frommonomeric styrene by an emulsion polymerization operation to give aproduct which is water-white and crystal-clear, and which has improvedstrength characteristics and heat distortion values over thoseheretofore obtainable by means of the casting techniques One of theresults flowing from our invention is that the polystyrene can beprepared in the matter of only a few hours without impairing any of itsdesirable qualities such as color, physical properties, etc. Inaddition..the temperatures employed in our process are relatively low,thus making our process economically attractive, especially since norigid temperature or other controls are necessary. These results are tobe contrasted with casting techniques which require many hours ofheating under rigidly controlled temperature conditions.

In accordance with our invention, the desirable results described aboveare effected by employing a particular combination of ingredients withinspecific ranges. One of the important features of our invention residesin the fact that we employ certain specific long-chain fatty acids toeffect emulsification in amounts heretofore believed too small to givethe desired results. Unexpectedly, we found that by employing .theseparticular acids in low concentrations, we were able to obtain acrystal-clear, water-white polystyrene free of discoloration, while atthe samev time effecting a satisfactory emulsification of thepolymerization system, without necessitating the removal of thelong-chain fatty acid or its salt. In addition, it was found that thepolystyrene thus prepared had heat distortion values and mechanicalstrength superior to those obtained by casting methods. In addition tothe requirement for the use of a particular fatty acid foremulsification, it was found that the desirable results described abovecould only be obtained by the use of a specific polymerization catalyst.namely, l-hydroxycyclohexyl hydroperoxide-l.

These requirements for successful attainment of the desired results wereentirely unexpected andinnowaycouldhavebeenpredictedfrom attempts to useindividual long-chain fatty acids other than the aforementioned acids,and other commonly used emulsion vinyl polymerization catalysts. Thus,for example, the use of lauric acidinan amountlessthanlpercentdidnotresult in any emuisification. Amounts in excessoi1percent,e.g.,2to3percentsumcientto give satisfactory emulsiiication,yielded products inferior color and strengths unless the acid or itssalt was removed by expensive and complex procedures after thepolymerization operation and before molding. The use of a fatty acidsuch as oleic acid which is commonly employed in emulsion polymerizationreactions also causes undesirable coloring of the polystyrene.

In contrast to the above, the use of myristic, palmitic and stearicacids, and mixtures of saturated aliphatic monocarboxylic acidscontaining from 12 to 18 carbon atoms having an average molecular weightof from 210 to 284, preferably, from 220 to 260, in amounts equal to atmost 1 per cent resulted in clear, water-white products which hadimproved color and physical properties and which did not require theremoval of the acid or its salts from the formed poly yrene. Thepresence in the polys yrene of the fatty acid had the additionaLeifectof acting as a parting agent on molding.

Furthermore, it was found that the use of other emulsion polymerizationcatalysts in place of l-hydroxycyclohenl hydroperoxide-1 either failedto effect any polymerization in our emulsiilcation system (hydrogenperoxide) or gave a dark, yellowish brown color (potassium persuifate),or caused excessive agglomeration and the formation of too low molecularweight polymers (tertiary-butyl hydroperoxide).

The myristic, palmitic, stearic or mixture of long-chain fatty acids isgenerally present in an amount equal to 1 per cent or less, e. g., from0.3 per cent to 1 per cent, preferably from 0.4 to 0.8 per cent, byweight, based on the weight of the styrene Although the amount ofl-hydroxycyclohexyl hydroperoxide-l may be varied within broad ranges,nevertheless, we have found that optimum results are obtained when thispolymerization catalyst is present in an amount equal to from 0.1 to 2per cent, preferably from 0.25 to 1 per cent, by weight, based on theweight of the monomeric styrene. We have also discovered that certainunexpected advantages are obtained by adding the catalyst incrementally.Thus, we have found it advantageous to add from to per cent of thecatalyst at the start of the emulsion polymerization, thereafter addingfrom to per cent of the catalyst after about one hour, and the remainderof the catalyst after about 2 hours. By means of this progressiveaddition ofthe catalyst, it has been found possible to increase the rateof polymerization and improve the yield considerably without impairingthe properties of the polystyrene in any way.

In the practice of our invention, we have found that the introduction ofas little as 0.25 part, e. g., from 0.25 to 3 parts, of a water-solublecopper or silver salt per million parts of water gave a satisfactorypolymerization rate and tially a 4 complete conversion of the styrene topo ystyrene. In addition, such introduction of the metal salts aided incontrolling the molecular weight of the polystyrene. Thus, we may usesuch water-soluble salts as, for example, copper sulfate (CuSO4-5HaO),silver nitrate, copper nitrate [for example, Cu(N0:):-3H:Ol, etc. Theterm "water-soluble" when employed in connection with the foregoinginorganic copper and silver salts is intended to mean those salts whichhave good solubility in water, for example, are soluble in the ratio ofat least 25 parts of the salt 1;? 100 parts of water, when measured ataround We have also found that the ratio of monomeric styrene to water(preferably distilled or deionized) in the emulsified system plays animportant part in determining the rate of pobmerization, the yield andtype of product obtained, as well as ease of preparation of the polymer.Thus, on a weight basis-we have found that for each part of monomericstyrene we may advantageousiy employ from 1.5 to 2.8 parts water perpart styrene. Amounts of water in excess of the above ratio resulted inlow yields of the po mer and the use of smaller amounts of waterresulted in undesirable increases in viscosity with attendant stirringdimculties as well as the inability to control adequately thetemperature of the reaction mixture.

In determining the average molecular weight of mixtures of theaforementioned saturated allphatic monocarboxylic acids, dueconsideration must be given both to the respective molecular weight andthe amount (or weight) of the individual acids comprising the mixture ofthe long chain fatty acids as compared to the ratio of the total amount(or weight) of the mixture of acids and the average molecular weight tobe determined. More specifically, a formula covering this type ofcalculation is as follows:

Weight of acid A weight of is B Mo]. wt. of acid A mol. wt. of acid Btotal wt. of A and B average mol.wt. to be determined Among thealkali-metal hydroxides (which form soaps with the long-chain fattyacids which in turn act as the emulsifying agents for the styrene) whichmay be employed in effecting neutralization of the long-chain fatty acidor mixture of fatty acids may be mentioned, for instance, sodiumhydroxide, potassium hydroxide, lithium hydroxide, etc. We prefer to usepotassium hydroxide, since there is a minimum of a8- glomeration withthe use of this particular alkalimetal hydroxide.

The amount of alkali-metal hydroxide is preferably in an amount equal tofrom to 125 per cent of that required to neutralize the fatty acid oracids. Amounts below 85 per cent do not give satisfactory emulsions andamounts in excess of 125 per cent do not produce any beneficial effectsmerely making the emulson more alkaline. We have found that best resultsare obtained when neutralization is from to per cent complete or, forthe upper limit, a 5 per cent molar excess of the alkali-metal hydroxideover that required for complete neutralization is preferried.

In effecting the emulsion polymerization, it is desirable that certainprecautions as to temperature limitations be taken. Thus the use of ahigh temperature will cause undesirable discoloration and appreciablylower heat distortion values. In addition, the viscosity of the latexincreases with the use of higher temperatures. We advantageously employtemperatures ranging from 50 to 90 0., preferably from 60 to 75 C., toretain better control of the reaction and to obtain a more uniformproduct. The time required for complete polymerization will of coursedepend on many factors, e. g., temperature, catalyst concentration,presence or absence of water-soluble copper or silver inorganic salts,etc. Generally, under optimum conditions of reaction, we may employ fromtwo to six hours for completion of the emulsion polymerization reaction.We have found however, that the use of longer times of reaction mayresult in polymers having improved properties over polymers prepared inaccordance with our claimed process which have been emulsion polymerizedfor shorter periods of time.

Thus, by conducting the emulsion polymerization at about 60-64 C. forapproximately 21 hours, we have obtained transfer molded polystyrenehaving heat distortion temperatures of the order of 105 C., a flexuralstrength of about 14,400 p. s. i., and an impact strength ofapproxmately 0.12 to 0.17 ft. lb. However, the practical reasons, it isusually desirable to conduct the emulsion polymerization for the leastpossible time consistent with the obtaining of acceptable improvedproperties over that now obtainable with polystyrene prepared by castingtechniques.

The manner in which our process may be practiced may be varied withinwide limits depend.- ing upon many factors, for instance, the amount andtype of long-chain fatty acid employed, the alkali-metal hydroxide used,the water-to-styrene ratio, the per cent of l-hydroxycyclohexylhydroperoxide-l, etc. The following description is a preferred methodfor effectin the emulsion polymerization, it being understood that we donot intend to be limited in any Way by this description:

The styrene, water (dc-ionized or distilled) and the alkali-metalhydroxide are heated together for a short time under vacuum at atemperature of about 40 to 50 C. to remove any dissolved gases, such asair, from the materials. The vacuum is then broken by admitting nitrogengas; thereafter, the long chain fatty acid or mixture of fatty acids,together with any copper or silver salt (if employed) are added, Thereaction mixture is then heated to a temperature of about 60 to 70 C.and part of the l-hydroxycyclohexyl hydroperoxide-l is added. A vacuumis then applied to the reaction vessel in order to cause the contents toreflux. After about 1 hour of reaction, the second portion of thepolymerization catalyst is added, the refluxing continued for anotherhour and at the end of this time the balance of the catalyst is added tothe reaction mass. At the end of an additional 1 to 3 hours of heatingat 60 to 70 C., it will be found that the styrene is from 90 to 97 percent polymerized and the reaction is substantially completed. We havefound that the pH of the emulsion (which can be regulated by the amountof alkali-metal hydroxide) at the start of the reaction shouldpreferably be from about to 11 initially, and at the end of the reactionranges from about 7.5 to 8.0.

The emulsion is then preferably though not essentially steam distilledto remove the unpolymerized styrene (if any) as completely as possible.The emulsion is broken by running it into an approximately equal volumeof water containing sumcient acid, for example, hydrochloric acid, toneutralize the alkali-metal hydroxide previously added. The slurry thusformed is boiled until the original fluffy precipitate caused by addingthe emulsion to the acid-water solution is converted to a densesand-like precipitate. The precipitated polystyrene is then isolated byfiltration, washed with water, and dried. It is then ready for molding.

In order that those skilled in the art may better understand how thepresent invention may be practiced, the following examples are given byway of illustration and not by way of limitation. All parts are byweight. Because of the difliculty of obtaining pure myristic acid, itwas necessary to use myristic acid containing the additional impuritiesin the following per cents, by weight, which in no way affected thefinal results:

Per cent Myristic acid 92.1 Laurie acid 5.5 Palmitic acid 2.4

Flexural and impact strength tests on the molded product were conductedon a Louis Schopper Dynstat machine.

The heat distortion temperatures of the various samples were measuredusing a modified A. S. T. M. procedure whereby smaller samples thanthose required by the regular A.S. T. M. tests were employed. Moreparticularly, instead of using a 5" x x /g" bar, a smaller test specimenx x (dynstat sample) was employed. In addition, a 5-kg. weight wassubstituted for the standard 2.5-kg. load. With the above exceptions,the procedure was identical with A. S. T. M. test method D648-45T. Acomparison of the results of the modified heat distortion test with thestandard A. S. T. M. test showed that the results were essentially thesame.

Example I In this example varying amounts of myristie acid were employedto show the effect of myristic acid concentration. The followingformulations were employed. The per cent, by weight, myristic acid usedwas based on the weight of the monomeric styrene. The water used in thefollowing samples contained 1 part CuSO4-5H2O per million parts ofwater.

Volume Volume 4 Sample Weight Myrlstic Weight 1 0.432 N Distilled 1 No.Styrene Acid KOH water (.atalyst Grams Per cent Cc. Cc. Grams 1l-hydroxycyclohcxyl hydroperoxide-l.

The styrene, water and potassium hydroxide solution were placed inindividual pressure vessels, evacuated to remove any trapped air and thevacuum released with nitrogen. The myristic acid and l-hydroxycyclohexylhydroperoxide-l were then added, the bottles closed, and thereaftershaken at 64 C. for 5 hours. The latices were diluted with two volumesdistilled water, and coagulated with a 50 per cent excess ofhydrochloric acid. The slurry thus obtained was granulated by heating toto C., filtered,

or I 3 and washed several times with hot water, and the granularpolystyrene was then dried. Analysis of the yields of the polymer showthat they ranged fronrabout 93 to 96 per centof the theoretical. Samplesof each of the dried powders were then molded both by transfer andinjection moldings. and heat distortion temperatures, flexuralstrengths, and impact strengths were determined on the molded samples.Following are the results of these tests:

Example 111 This example illustrates the elect 01', using a long-chainfatty acid whose molecular weight is below the critical 210 averagemolecular weight required for mixtures of the requisite long-chainacids. More particularly, this example is concerned with the use oflauric acid in concentrations equivalent to the concentrations of the 10myristic acid found in Example I above.

'iransier Molding Injection Molding Molec- Sample N o Distor- Distor-Weight on Flerural Impact an Flasnral Impact Tam Strength Strength TamStmlgth Strength 90 12, 300 0. no N 10,) 0. 13 90 11, 5G) 0. 01 96 10,we 0. 11 99 ll, 3!!) 0. 07 94 9, 0. 0o 92 8, (I!) 0. 04 94 8, ill) 0. 0797 9, m 0. N '02 8, M 0. (B

In addition to the results found above which indicate the improvedmechanical propertiu possible by the use of amounts of myristic acidequal to 1 per cent or less, it was found that Styne whereas moldedSamples 1, 2 and 3 Q m as cellent clarity and were water-white in color,Samples 4 and 5 were hazy in color and in addition showed signs ofyellowing and discoloration.

Example II v This example illustrates the advantage obtained by addingthe emulsion tion catalyst, i. e., l-hydroxycyclohexyl hydroperoxide-l,in incremental steps. The results should be contrasted with thoseobtained in Example I inwhich the catalyst was added all at one time.

styrene grams 250 0.425 N KOH solution ....co 14.2 -Distilled water cc610.8 Myristic acid ...grams 1.5 Solution containing 0.06 gramCuSO4'5H2O per 100 cc. water cc 1.04 l-hydroxycyciohexyl hydroperoxide-1"grams..- 1.25

The styrene, potassium hydroxide, and water were placed in a 3-neckliter flask equipped with a water-sealed stirrer, thermometer well, and

stopper and heated to 50 C. The flask was evacuated through a condenserto give a reflux and the vacuum released with nitrogen. The coppersulfate solution was added to the stirred mixture and the temperaturebrought up to 70 C. at which time the myristic acid and 0.25 gram of thel-hydroxycyclohexyl hydroperoxide-l were added to start the reaction.Throughout the reaction the temperature was maintained at around 70 C.After about 60 minutes of reaction an additional 0.50 gram of catalystwas added and about 60 minutes later the remainder of the catalyst wasadded. At the end of about 137 minutes of total reaction time, it wasfound that the yield of polystyrene was 94.7 per cent based ontheoretical amount. This result is to be contrasted with a yield of 93.1per cent obtained after five hours of reaction as was required inExample I when the emulsion polymerization catalyst was added all atonce.

Sample e flampb 7 he "grams" 250 a 0.425 N KOH solution cubicoentlmeiem. l6. 8 21.0 Distilled water ..do one 2 601. 1 Laurie acid...grams.. 1. s 2. 5 Water solution containing 0.00 grain CilBOrfiHsO per100 cc. water cubic centimeters 1.04 l. M l-hydroxycyclohexylhydroperoride-l grams" 1. 26 l. 3

The procedures for adding the catalyst and effecting the emulsionpolymerization were identical with that employed in Example II. At theend of about five hours of heating at the temperature stipulated in theaforementioned Ixampie If, it was found that the yield of polystyrene inSample 6 was about 16.8 per cent, and in Sample 7 21.9 per cent of thetheoretical.

Example 17 In this example, two runs were made in which the ingredientsemployed were identical, with the exception that in Sample 8 there wasemployed 1.5 grams stearic acid and in Sample 9 1.5 grams palmitic acid,each acid corresponding to 0.6 per cent, by weight, of the monomericstyrene employed therein. Otherwise the formulations were as follows:

Sample 8 Sample 9 Styrene -.grams 250 0.425 N KOH solution cubiccentimeters. 1i. Distilled water... do 613. Long-chain fatty acid.grams 1. Water solution containing 0.06 gram CuS04-5H10 per 100 cc.water cubic centimeters. l.

l-hydroxycyclohexyl hydroperoxide-l 1 25 gram- The incremental additionof catalyst and emulsiflcation were carried out in exactly the samemanner as employed in Example II. In each case, polymerization was morethan per cent complete after 137 minutes. The polystyrene was isolatedusing the procedure employed in Example I. The isolated polymer waswashed with hot water and dried, and samples of each u material wereinjection molded and the molded good clarity and exhibited nodiscoloration. Following are the results of these tests:

Example VI In this example, mixture containing 3 and 4 fatty acids ofthe requisite type were prepared and employed in the preparation ofpolystyrene M1 1 Fl um] I PM He Dis 5 by emulsion polymerization. ineach casein the Sample No. t f h m tom following samples, 250 gramsstyrene, about 611 e g mm was I 0 cc. distilled water, 1.04 cc. solutioncontaining 0.06 e grams CuS04.5Hz0 per 100 cc. water, and 1.25 s 193,00011,100 0.15 94 grams of l-hydroxycyclohexyl hydroperoxide-l 9 237,000L400 94 m were employed. In addition, the samples con- 4 tained thefollowing additional ingredients: Annealing of the molded samples for 64hours at 85 C. raised the heat distortion temperature 3 1 13 s 1 14 ofSamples 8 and 9 to 104 c. and 103 c., respectively' 15 N l onsolution.cubiooentimeters. 13.98 v 13.40 Example V 1 113 1181132 1 8111(31% tea 0. 0.4 In this example, mixtures of myristic acid 2111:1210 ma:2 393 13 and lauric acid were employed in varying proportions toillustrate the eiiect of using mixtures The average molecular weight f tblend of of acids whose average molecular weight is above the acids insample 13 was 240 and in sample 14 and below an average molecular 0f wasof the ample was prepared in the same manner as employed in Example II.At the end of 197 minutes Sample 13 showed a s 1 s 1 s 1 it l l 1 2yield of about '17 per cent of the theoretical and Sample 14 showed ayield of about 92.8 per cent giY2g8ei6fi -it grams 250 250 250 of thetheoretical.

- Each of the latices was filtered after cooling b t a 21.1 26.7 25.9 nlst l a wager" m 3:03. 593. 688.7% ss aa and then precipitated asfollows: 500 cc. of the grams" latex and 1000 cc. distilled water werestirred to- L uri a- 2.0 1.75 1.25

a cm s g am gether in a 3-l1ter beaker on a hot plate. Therecusoi'mgo ggg ggggggg v L04 L04 L04 after, 10 cc. of 2 N HCl was slowly added to thel'hydroxycyclohexylhydroperoxide-l 1 25 1 25 1 25 stirred mixture andthe coagulated polymer grams" I 1 ht f vigorously stirred to form a fineslurry. The mixt i r iffi tn -i c 206 210 211 ture was then heated to7580 C. at which time the polymer granulated. It was then filtered, 5The incremental addition of the catalyst and K 5 33232? fgi about 1hoursin circulat the emulsion polymgrizafiqn of the polymer t Samples ofeach of the dried polymer powders each case was identwal with thatemployed in 4.0 were injection molded at about 186L204. Q head ExampleIsolatlon of w polymers was temperature and a temperature of 50 C. inthe gccomplislhed the techmque shown in mold. These samples were testedfor fiexural xample and im act stren ths and heat distortions with Atthe end of from 166 to 175 minutes, it was the fongwing resins: foundthat polymerization of Samples 11 and 12 had progressed to from 92 to 97per cent of the F] m I m H t theoretical amount. Sample 10 had onlypolysample stfe it gth S e lgth 10 21011 merized to 60.5 per cent of thetheoretical after 239 minutes, thus indicating the marked effect 0. Ofusing average 111018011121 weights Of mixtures of the acids havingvalues of and above 210. Mechanical and heat distortion tests conductedon Each of the samples had excellent clarity, were 3 plfgces samples 11and 12 showed crystal clear and waterwhite, and exhibited no 6 0 owmgresu evidence of discoloration whatsoever.

H tDlsm Example VII ea 1- sample 3. 3.31 tion p This example illustratesthe effect of using a still other mixtures of long-chain fatty acids 00having an even number of carbon atoms and n 10,600 M5 containing from 12to 18 carbon atoms whose 12 11,200 94 average molecular weight is equalto from 210 to Examplel5 Example 16 Example 17 Example 18 Styrene rams250 250 250 250 Distilled water cubic centimete 600.5 610.4 13.87 13.50.418N KOH snlnfinn rln 14.5 13.6 609.1 611.3 Aqueous solutioncontaining 0.06 gram 011804.5H20 per cc. water i cubic centimeters" l.04 1. 0 1. 0 1. 0 Laurie acid grams 0. 725 Myristic acid (in 1.0 1.0 0.75 Palmitic acid do 0. 5 0. 75 Stearlc Mi do 0. 775 0. 5l-hydroxycyclohexyl hydroperoxide-l do. 1. 25 1. 25 1. 25 1. 25 Averagemolecular weight of acids 236 250 242 246 In each case the styrene.water, copper sulfate, and potassium hydroxide solutions were mixedtogether and heated to 50 C.. evacuated to give a reflux and the vacuumreleased with nitrogen. Attheendofthistimeofigramofeachmixture of thefatty acids was added and the mixture heated with stirring to 70 C. Atthe end of one hour an additional 0.50 gram of the respective catalystmixture was added and after an addiwater, we have obtained polystyrenehaving nexural strengthsrsnging from 10,800 to 14,000 p. s. i. and heatdistortion temperatures of around 97 C. For more complete details of theelect of using copper sulfate, attention is directed to many of theforegoing examples.

In the following example are found testresults establishing theadvantage of using a certain ratio of monomeric styrene to water in theemultional 80 minutes of heating at about 20 C. the 10' sified system.

Example VIII sample weight We t Volume Volume Waterweight No. Styrene m2 333" Catalysu Gram Grams Ce. Gram 19.... 200 1.2 12.8 687.6 3.011 1.02) 210 1. 2 12.3 487. 7 2. :1 1. 0 2!] 1.2 12.3 427.7 2.2:1 1.0 200 1.212.3 347.7 1.8:1 1.0 200 1.2 12.3 37.7 1.5:1 1.0 2i.. 2D 1. 2 l2. 3 187.7 1. 0:1 1. 0

1 i-hydroxycyclohexyl hydroperoxide-l.

remainder of the catalyst was added. At the end of the following timesthe indicated per cent yields were obtained based on the theoretical:

The styrene, water, and KOH solution were placed in pressure reactorsand evacuated to free the mass from dissolved gases. The vacuum wasreleased with nitrogen and the myristic acid and Reaction Per Centl-hydroxycyclohexyl hydroperoxide-l were added. Sample No. Timein YieldThe reactors were closed and heated with shak- Minms ing at 70 C. forfour hours. Following are the percentage yields obtained in each case:is 210 925 is. 198 00.6 g Sample No. gf

Transfer molded samples of each of the isog; W5 lated products preparedabove were tested for 21 9418 ilexural strengths and heat distortiontempera- 5f gg-g tnres with the following results: 2L 9% o mum]HeatDlstor- The latices were diluted with water and pre- Strengthcipitated with a 50 per cent excess 1101. Each slurry was granulated byheating, and thereafter filtered and washed with hot water. Molded is11,700 94 samples were prepared by injection molding from i; 3% 8% eachof the precipitated polymers. These moldedrsIlZ'IIIIIIIIIIIIIIIIIIIIIIIII 101400 96 samples were tested for heatdistortion temperatures. flexural strengths, and impact strengths. 1 wBecause of the low yield, no samples were molded The various moldedsamples had excellent color and clarity comparableto that obtained usingmyristic acid alone.

In the practice of our invention, as stated previously, we have found itdesirable to employ water-soluble silver and copper inorganic salts. Theuse of these salts is not absolutely essential in obtaining polystyrenehaving the desirable properties discussed previously. However, we havefound that the presence of these silver and copper salts increases therate of polymerization so that lower temperatures and shorter periods oftime are required for eifecting the polymerization of the styrene toyield the desired products.

We have found that good results are obtained using concentrations of thecopper and silver salts in the range of from about 0.25 to 5 parts ofthe salt per million parts of water. The preferable 70 range is around0.5 to 2.0 parts of the salt per million parts of water. The use oflarger than 5 parts per million gave a slow rate and lncompletepolymerization. Using, for example, from 0.5 to 2.0 parts CilSO4'5H2Oper million parts of from run 19. Following are the results of thetests:

In each case the molded samples had excellent clarity and were free ofcolor. However, the use of less than a 2.5:1 water-monomer ratioincreased the viscosity of the emulsified mixture to an undesirableextent and made stirring and heat removal therefrom diillcult.

Example IX This example embraces the preparation of polystyrene on apilot plant scale employing our claimed emulsion polymerization process.The polystyrene obtained in this case was molded and 13 tested usingstandard AS'I'M mechanical strength and heat distortion tests. Forcomparison, tests were also conducted on two of polystyrene availablecommercially from two diiierent sources and which are produced bycasting methods.

Weight Styrene ..lbs... 47.3 Deionized water lbs 114.4 Myristic acidgrams 126.3

inch vacuum. applied for (to 5 minutes to the system through a condenserattached. to the kettle. The vacuum, was released with nitrogen and thekettle opened. reached about C... the myristic acid and 21.8

grams of the catalyst were added. the kettle I sealed, and brought toacontrolled vacuum oi 18 to 19 inches which maintained a fairly constantreflux temperature of the mass at around 61. to C. throughout thereaction.- Aiter one hour. the vacuum was released, and 43.6 grams ofcatalyst were added and the mass again heated under vacuum at theaforementioned temperature. At the end of 2 hours, the vacuum was againbroken and the final amount of catalyst (43.6 grams) was added. thekettle closed and again heated under vacuum for an additional hour. Atthe end of this time (3 hours total reaction time) the vacuum wasreleased and about 3.2 per cent unpolymerized styrene was removed bystripping.

The latex was then added slowly to an amount oi water containing a 25per cent excess of hydrochloric acid and heated to coagulate thepolystyrene slurry to a sand-like product. The polymer (obtained inabout a 96 per cent yield) was filtered, washed with boiling water, anddried at about 120 C., and densiiied by passing the same throughcalender rolls to give a. clear, densified sheet. The sheet was brokeninto sections and ground to give a suitable molding composition. Thismolding compound (identified as Sample No. 25) and two commerciallyavailable polystyrenes produced by casting (identified by Samples 26 and27, respectively) were injection molded in an injection press whereinthe head-temperature was around 250 C. The samples were molded in theform of test specimens whose dimensions and shape were the same as thoserequired for conducting standard ASTM tests. In each case,crystal-clear, water-white, molded objects were obtained which were freeof discoloration. Following are the results of these tests on the threesamples:

Test Sample 25 Sample 26 Sample 27 Impact Oharp Unnotched y ft. lbs. 12+ 1.35 1.88 Impact Izod Unnotched ft. lbs.. 1.83 0.97 l. 24 FiexnralStrengtb np. s. i. 12, 900. 10, 100 10, 300 Tensile Strcngth -.p. s. i7, 516 6, 200 6, 320 Heat Distortion ..C 91 78 i Reading was in excess012 ft. lbs.

When the temperature It will, of course. be apparent to those skilledinthe art that other modifying ingredients, for example, saturatedaliphaticmercaptans. for

. instance. dodecyl mercaptan, .etc which cause V certaintdesirableimprovements in the final polymerized styrenemay also be added duringthe polymerization operation without departing from the scope of ourinvention. we have found" itadvantageous to add from 0.05 to 0.5 percent, by weight, based on'the weight of the. styrene of dodecylmercaptan in, order to obtain a polystyrene having' improved plasticitycharacteristics. The addition of this material in no way retards thecourse of the polymerization and does 1 not change the properties of thepolymers undesirably. I

Polystyrene prepared in accordance with'our claimed process isparticularly amenable to injection and transfer molding due to itsoutstanding plasticity and fluidity under molding conditions. Eventhough the properties of the molded products are superior to polystyreneprepared by thev casting method. nevertheless, i t is not neces--apparatus and conditions commonly employed are satisfactory.

The molded products obtained from the polystyrene prepared in accordancewith the disclosures and teachings stated above have eminent use asdielectric materials, for example, as spacers for coaxial cables, asinsulating materials for electrical conductors, etc. Because of itsoutstandingheat distortion properties and mechanical strengths,polystyrene prepared in accordance with our process finds extensive usefor decorative electrical light fixtures.

The polystyrene prepared in accordance with our process may be alsomodified with various ingredients, for example, dyes, pigments, or othermodifying resins both natural and synthetic. Because of the fact thatthe polystyrene is obtained as a finely dispersed suspension, it canreadily be dyed or pigmented by merely adding the latter to the wateremulsion and mixing the composition thoroughly.

What we claim asnew and desire to secure by Letters Patent of the UnitedStates is:

l. The method of producing a crystal-clear polystyrene free ofdicoloration and having a heat distortion temperature of at least 90 C.,which method comprises heating anemulsified mass comprising (l) styrene,(2) water, (3) an alkali-metal hydroxide suflicient to neutralize atleast per cent of the fatty acid component of (4), (4) a fatty acidcomponent selected from the class consisting of (a) myristic acid, (b)palmitic acid, 60 (c) stearic acid; and (d) mixtures of saturatedaliphatic monocarboxylic acids having an even number of carbon atoms andcontaining from 12 to 18 carbon atoms whose average molecular weight isequal to from at least 210 to less than 284, said fatty acid componentbeing present in an amount equal to from 0.3 per cent up to andincluding 1 per cent, by weight, based on the weight of the styrene, and(5) a polymerization catalyst comprising l-hydroxycyclohexyl hydro- 70peroxide-1.

2. The method of producing a. crystal-clear polystyrene free ofdiscoloration and having a heat distortion temperature of at least 0.,

which method comprises heating an emulsified 1 75 mass comprising (1)styrene, (2) water, and (3) sary'to employ any un'usual'moldi'ngconditions to obtain these properties since injection molding 15 from0.3 to 1 per cent, by weight, myristic acid based on the weight of (1),(4) an alkali-metal hydroxide suillcient to neutralize at least 85 percent oi the myristic acid, and a polymerization catalyst comprisingl-hydroxycyclohexyl hydroperoxide1.

3. The method of producing a crystal-clear polystyrene free ofdiscoloration and having a heat distortion temperature of at least 90C., which method comprises heating an emulsified mass comprising (1)styrene, (2) water, and (3) from 0.3 to 1 per cent, by weight, palmiticacid based on the weight of (1). (4) an alkali-metal hydroxidesuillcient to neutralize at least 85 per cent of the palmitic acid. and(5) a polymerisation catalyst comprising l-hydroxycyclohexylhydroperoxide-l.

4. The method of producing a crystal-clear polystyrene free ofdiscoloration and having a heat distortion temperature of at least 90C., which method comprises heating an emulsified mass comprising (1)styrene, (2) water, (3) from 0.3 to 1 per cent, by weight, based on theweight of (1) of a mixture of saturated aliphatic monocsrboxylic acidshaving an even number of carbon atoms and containing from 12 to 18carbon atoms whose average molecular weight is equal to from at least210 to less than 284, (4) an alkalimetal hydroxide suflicient toneutralize at least 85 per cent of the acids of (3), and (5) apolymerization catalyst comprising l-hydrowcyclohexyl hydroperoxide-l.

5. The method of producing a crystal-clear polystyrene free ofdiscoloration and having a heat distortion temperature of at least 900., which method comprises heating an emulsified mass comprising (1)styrene, (2) water, (3) from 0.3 to 1 per cent, by weight, based on theweight of (1), of a fatty acid component selected from the classconsisting of (a) myristic acid, (b) palmitlc acid, (0) stearic acid,and (d) mixtures of saturated aliphatic monocarboxylic acids having aneven number of carbon atoms and containing from 12 to 18 carbon atomswhose average molecular weight is equal to from at least 210 toless than284, (4) an alkali-metal hydroxide suflicient to neutralize at least 85per cent of the acids 0! (3), (5) a polymerization catalyst comprising l-hydroxycyclohexyl hydroperoxide-l, and (6) a salt selected from theclass consisting of water-soluble, inorganic copper salts andwater-soluble inorganic silver salts.

6. The method as in claim 5 wherein the watersoluble salt of (6) iscopper sulfate.

7. The method of producing a crystal-clear polystyrene free ofdiscoloration and having a heat distortion temperature of at least 90(3., which method comprises heating at a temperature of from 50 to 90 C.an emulsified mass com- 'prising (1) styrene. (2) water, the water beingpresent, by weight, in an amount equal to from 1.5 to 2.8 parts waterper part styrene, (3) from 0.3 to 1 per cent, by weight, based on theweight of (l), of a fatty acid component selected from the classconsisting of (a) myristic acid, (b) palmitic acid, (0) stearic acid,and ((1) mixtures of saturated aliphatic monocarboxylic acids having aneven number of carbon atoms and c0ntaining from 12 to 18 carbon atomswhose average molecular weight is equal to from at least 210 to lessthan 284, (4) potassium hydroxide suillcient to neutralize at least 85per cent of the acids of (3), and (5) a polymerization catalystcomprising l-hydroxycyclohexyl hydroperoxide-l.

8. The method of producing a crystal-clear polystyrene free ofdiscoloration and having a heat distortion temperature of at least 90C., which method comprises heating at a temperature of from to 90 C., anemulsified mass comprising (1) styrene, (2) water, the water beingpresent, by weight, in an amount equal to from 1.5 to 2.8 parts waterper part styrene, (3) from 0.3- to 1 per cent. by weight, based on theweight of (1) of myristic acid, (4) potassium hydroxide suflicient toneutralize at least 90 per cent of the myristic acid of (3), and (5) apolymerization catalyst consisting of l-hydroxycyclohexylhydroperoxide-l.

9. The method of producing a crystal-clear polystyrene free ofdiscoloration and having a heat distortion temperature oi at least 900., which method comprises heating an emulsified mass comprising (1)styrene, (2) water, (3) potassium hydroxide suiilcient to neutralize atleast 85 per cent of the fatty acid component of (4), (4') a fatty acidcomponent selected from the class consisting of (a) myristic acid, (b)palmitic acid, (0) stearic acid, and (d) mixtures of saturated aliphaticmonocarboxylic acids having an even number of carbon atoms andcontaining from 12 to 18 carbon atoms whose average molecular weight isequal to from at least 210 to less than 284, said fatty acid componentbeing present in an amount equal to from 0.3 per cent up to andincluding 1 per cent, by weight, based on the weight of the styrene, and(5) a polymerization catalyst consisting of l-hydroxycyclohexylhydroperoxide-l.

10. The method of producing crystal-clear polystyrene free ofdiscoloration whose heat distortion temperature is at least 90 C., whichmethod comprises heating at a temperature of from to C. an emulsifiedmass comprising (1) styrene, (2) water, the water being present, byweight, in an amount equal to from 1.5 to 2.8 parts water per partstyrene, (3) from 0.4 to 0.8 per cent, by weight, myristic acid based onthe weight of styrene, (4) potassium hydroxide sunlcient to neutralizeat least 95 per cent of the myristic acid, (5) from 0.25 to 1 per cent,by

weight, based on the weight of the styrene, of a polymerization catalystconsisting of l-hydroxycyclohexyl hydroperoxide-l, and (6) coppersulfate, the copper sulfate being present in an amount equal to from0.25 to 3 parts per million parts of water.

11. The method as in claim 10 wherein the l-hydroxycyclohexylhydroperoxide-l is added incrementally as follows:

From 15 to 25 per cent at the start of the emulsion polymerization;

From 35 to 50 per cent after approximately one hour of reaction;

The remainder of the catalyst after about two hours of reaction.

12. The method of preparing a polystyrene which on molding iscrystal-clear, free of discoloration and has a heat distortiontemperature of at least 0., which method comprises heating at atemperature ranging from 50 to 90 C. an emulsified mass comprising 1)styrene, (2) water; (3) from 0.3 to 1 per cent, by weight, based on theweight of (1) of a mixture of iauric acid, myristic acid, and stearicacid, wherein the average molecular welght of the acids is equal to atleast 210 and less than 284, (4) potassium hydroxide sufficient toneutralize at least per cent of the mixture of acids in (3) (5) from0.25

75 to 1 per cent, by weight, based on the weight of 17 the styrene, ofl-hydroxycyclohexyl hydroperoxide-1, and (6) CuSO4-5HzO wherein thelatter is present in an amount equal to from 0.25 to 3 parts per millionparts of water.

EDMOND F. FIEDLER. GLENNARD R. LUCAS.

18 REFERENCES CITED The following references are of record in the fileof this patent:

Brajnikoff: (pages 230-238).

Hohenstein et a1: India Rubber World, vol. 111, pp. 173-177, Nov. 1944.

Plastics (London), July 1942,

1. THE METHOD OF PRODUCING A CRYSTAL-CLEAR POLYSTYRENE FREE OFDICOLORATION AND HAVING A HEAT DISTORTION TEMPERATURE OF AT LEAST 90*C.,WHICH METHOD COMPRISES HEATING AN EMULSIFIED MAS COMPRISING (1) STYRENE,(2) WATER, (3) AN ALKALI-METAL HYDROXIDE SUFFICIENT TO NEUTRALIZE ATLEAST 85 PER CENT OF THE FATTY ACID COMPONENT OF (4), (4) A FATTY ACIDCOMPONENT SELECTED FROM THE CLASS CONSISTING OF (A) MYRISTIC ACID, (B)PALMITIC ACID, (C) STEARIC ACID, AND (D) MIXTURES OF SATURATED ALIPHATICMONOCARBOXYLIC ACIDS HAVING AN EVEN NUMBER OF CARBON ATOMS ANDCONTAINING FROM 12 TO 18 CARBON ATOMS WHOSE AVERAGE MOLECULAR WEIGHT ISEQUAL TO FROM AT LEAST 210 TO LESS THAN 284, SAID FATTY ACID COMPONENTBEING PRESENT IN AN AMOUNT EQUAL TO FROM 0.3 PER CENT UP TO ANDINCLUDING 1 PER CENT, BY WEIGHT, BASED ON THE WEIGHT OF THE STYRENE, AND(5) A POLYMERIZATION CATALYST COMPRISING 1-HYDROXYCYCLOHEXYLHYDROPEROXIDE-1.